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Question on SM in yorkies

I am posting this on behalf of Loreta Serafini. I replied privately to her and have included some of my response below. She is not a member but she can read all the discussion online, and I know would appreciate others' perspectives. I've crossposted to the SM support list as well, http://groups.yahoo.com/group/CKCS-SM-support/

On 28 Jul 2006, at 15:40, ozyorkshires wrote:

I am not a member of your list but would you kindly post this to the
list - Thanks

Has anyone heard of cases of syringomyelia in Yorkies? Would it be
genetic in Yorkies as it might be in Cavaliers? Are both parents
required to be carriers ie. is it a simple recessive? Can one parent
be a carrier and the other not? Is head/neck scratching always a
symptom? Are seizures ever present in an affected?
Thanks in advance,

Loreta Serafini
Oz Yorkshire Terriers.

<<Hi Loreta:

I will also post this to the CKCS-SM-support list with part of this reply; but I can give a quick answer to your questions and others may wish to add more: yes, it is known in yorkies and other small breeds. The symptoms would be the same as in cavaliers. Seizures can be a symptom and would generally indicate a more severe form of SM (though seizures could also indicate epilepsy or other conditions too; a neurologist would need to MRI for diagnosis). Inheritance is not yet understood but it seems to be a polygenetic recessive trait, which makes it very hard to pinpoint. There is a genome scan underway on cavaliers for SM which should help clarify this question, if not fully answer it. However SM can be caused by other things such as a traumatic blow to the head/neck. Head and neck scratching is a symptom in fewer than 50% of affected dogs according to neurologists and many SM affected dogs do not scratch at all. There is a lot of information, almost all of which would apply to any dog with SM, at my information site: htttp://sm.cavaliertalk.com.

I remember on the A/C list that there were quite a few Yorkies with SM, perhaps you could direct her to that list, I have long since left but I'm sure others might have the link....I'm sure that Yorkies are affected just the same way as the Cavaliers, Mel had little Heather remember.....

Yorkies and other brachycephalic breeds are known to have "occipital
dysplasia", which is different from the "occipital hypoplasia" which
is the cause of SM in Cavaliers. Cavaliers are brachycephalic, too,
so they also can have occipital dysplasia.

The difference is that occipital dysplasia is an incomplete
ossification of the supraoccipital bone, causing a widening of the
foramen magnum. The more brachycephalic is the shape of the dog's
skull, the more likely there will be occipital dysplasia. This is
discussed on this webpage:http://www.cavalierhealth.org/syringomyelia.htm

Clare Rusbridge and Penny Knowler wrote a journal article about
Cavaliers having both occipital hypoplasia and occipital dysplasia:
Coexistence of occipital dysplasia and occipital
hypoplasia/syringomyelia in the cavalier King Charles spaniel. C.
Rusbridge and S. P. Knowler. J. Small Anim. Prac. Oct. 2006, 47
(10). It has not been published yet.